The wet milling technique is one of the key technologies for targeted setting of materials properties for the paint and varnish industry through to the food and pharmaceutical industry. Ceramic milling balls are used in stirred ball mills for wet milling a variety of materials, e.g. pigments, and for dispersing formulations. A substantial step forward in terms of the efficiency and contamination risk of such processes has already been achieved by the use of ceramic milling balls. In efforts being made to achieve more efficient processes and milling finenesses on the nanometer scale, the material density and thus the achievable energy input in the milling process play an important role in the wet milling process. Milling balls based on oxide ceramics which are available on the market at present have good wear resistance but the maximum density of commercially available milling balls, for example from Compagnie de Saint Gobain (www.zirpro.com), Jyoti Ceramic Industries Pvt. Ltd. (www.jyoticeramic.com) or Zircoa Inc. (www.zircoa.com), is less than 6.3 g/cm3 (as at 2013).
It is therefore an object of the invention to provide sintered balls having an increased density, greater wear resistance and greater durability.
This object is achieved by a sintered ball comprising tungsten carbide, WC, and partially stabilized zirconium oxide, nX:ZrO2.
Furthermore, the invention provides a powder mixture, a green body obtainable therefrom and also processes for producing the green body and the sintered ball from the green body.
Further preferred embodiments may be found in the dependent claims.
The invention is based on the idea of developing a process for producing milling balls which have the composition xVol. %-WC-yVol. %-nX:ZrO2 and after having been produced have material densities of greater than or equal to 6.3 g/cm3, high wear resistance and great durability.
The basis of the invention is formed by materials compositions comprising metallic hard material, namely tungsten carbide WC, and an oxide ceramic, namely partially stabilized zirconium oxide or zirconium(IV) oxide nX:ZrO2, hereinafter also referred to as zirconium oxide in the interest of simplicity, by means of which higher milling media densities can be achieved and thus higher energy inputs in milling processes and efficient milling finenesses on the nanometer scale can be obtained. Although such materials compositions are already known, for example from D. Jiang et al., ZrO2—WC nanocomposites with superior properties, J Eur. Cer. Soc. 27 (2007), 1247-1251, these have hitherto not been able to be processed to give milling media balls.